Setup:

• Flask-SocketIO==4.3.1
• python-engineio==3.13.2
• python-socketio==4.6.0

Make sure you restart your machine to not encounter errors.

Python Code -saved in D:Projects est_backgroundtask:

from flask import Flask, render_template, request
import pandas as pd
from flask_executor import Executor
import plotly
import plotly.graph_objs as go
from flask_socketio import SocketIO, emit
import json

global test_val
app = Flask(__name__)
socketio = SocketIO(app)
def create_plot(feature_importance):
    feature_importance=feature_importance.reset_index(drop=True)
    feature_importance=feature_importance.iloc[0:5]
    print(feature_importance)

    data = [
        go.Bar(
            x=feature_importance['Age'], # assign x as the dataframe column 'x'
            y=feature_importance['Name'], orientation='h'
        )
    ]

    graphJSON = json.dumps(data, cls=plotly.utils.PlotlyJSONEncoder)

    return graphJSON

@socketio.on("response")
def background_task_func():
    global test_val
    global plot
    socketio.sleep(10)
    data = {'Name': ['Tom', 'Joseph', 'Krish', 'John'], 'Age': [20, 21, 19, 18]}  
    test_val= pd.DataFrame(data)
    bar = create_plot(test_val)
    plot=bar
    if test_val.shape[0]>1:
        print(test_val)
        emit('response_output',plot ,broadcast=True)
        socketio.sleep(1)
        #return render_template('views/index_img_soc.html', plot=bar)
    
@app.route('/', methods=['GET'])
def index():
    global plot
    executor.submit(background_task_func)
    bar = create_plot(test_val)
    
    return render_template('views/index_img_soc.html', plot=bar)



if __name__ == "__main__":
    data ={'Name': [], 'Age': []}  
    test_val= pd.DataFrame(data)   
    executor = Executor(app)
    socketio.run(app) 

Html Code (saved in D:Projects est_backgroundtask emplateviews):

<script src="https://cdn.plot.ly/plotly-latest.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.6/d3.min.js"></script>
<div class="chart" id="bargraph">

    <script src="//cdnjs.cloudflare.com/ajax/libs/socket.io/2.2.0/socket.io.js" integrity="sha256-yr4fRk/GU1ehYJPAs8P4JlTgu0Hdsp4ZKrx8bDEDC3I=" crossorigin="anonymous"></script>
        <script type="text/javascript" charset="utf-8">

            var socket = io().connect('http://127.0.0.1:5000');
            socket.emit('response')
            socket.on('response_output', function(receiving_data) {
              var graphs = {{plot | safe}};
              Plotly.plot('bargraph',graphs,{});
            });
    </script>
</div>

Output:

WebSocket transport not available. Install eventlet or gevent and gevent-websocket for improved performance.
 * Serving Flask app "flask_background_app_img_soc2" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
127.0.0.1 - - [14/Jul/2021 11:45:01] "GET / HTTP/1.1" 200 -
Empty DataFrame
Columns: [Name, Age]
Index: []
2c6e85bb23aa4c83af37bc005a08837b: Sending packet OPEN data {'sid': '2c6e85bb23aa4c83af37bc005a08837b', 'upgrades': [], 'pingTimeout': 60000, 'pingInterval': 25000}
2c6e85bb23aa4c83af37bc005a08837b: Sending packet MESSAGE data 0
127.0.0.1 - - [14/Jul/2021 11:45:03] "GET /socket.io/?EIO=3&transport=polling&t=NgaPyfS HTTP/1.1" 200 -
2c6e85bb23aa4c83af37bc005a08837b: Received packet MESSAGE data 2["response"]
received event "response" from 2c6e85bb23aa4c83af37bc005a08837b [/]
127.0.0.1 - - [14/Jul/2021 11:45:03] "POST /socket.io/?EIO=3&transport=polling&t=NgaPyf-&sid=2c6e85bb23aa4c83af37bc005a08837b HTTP/1.1" 200 -
     Name  Age
0     Tom   20
1  Joseph   21
2   Krish   19
3    John   18
     Name  Age
0     Tom   20
1  Joseph   21
2   Krish   19
3    John   18
emitting event "response_output" to all [/]
2c6e85bb23aa4c83af37bc005a08837b: Sending packet MESSAGE data 2["response_output","[{"orientation": "h", "x": [20, 21, 19, 18], "y": ["Tom", "Joseph", "Krish", "John"], "type": "bar"}]"]
127.0.0.1 - - [14/Jul/2021 11:45:13] "GET /socket.io/?EIO=3&transport=polling&t=NgaPyg0&sid=2c6e85bb23aa4c83af37bc005a08837b HTTP/1.1" 200 -
     Name  Age
0     Tom   20
1  Joseph   21
2   Krish   19
3    John   18
     Name  Age
0     Tom   20
1  Joseph   21
2   Krish   19
3    John   18
2c6e85bb23aa4c83af37bc005a08837b: Received packet PING data None
2c6e85bb23aa4c83af37bc005a08837b: Sending packet PONG data None
127.0.0.1 - - [14/Jul/2021 11:45:28] "GET /socket.io/?EIO=3&transport=polling&t=NgaP_9E&sid=2c6e85bb23aa4c83af37bc005a08837b HTTP/1.1" 200 -
127.0.0.1 - - [14/Jul/2021 11:45:28] "POST /socket.io/?EIO=3&transport=polling&t=NgaQ2md&sid=2c6e85bb23aa4c83af37bc005a08837b HTTP/1.1" 200 -
2c6e85bb23aa4c83af37bc005a08837b: Received packet PING data None
2c6e85bb23aa4c83af37bc005a08837b: Sending packet PONG data None
127.0.0.1 - - [14/Jul/2021 11:45:54] "GET /socket.io/?EIO=3&transport=polling&t=NgaQ2nA&sid=2c6e85bb23aa4c83af37bc005a08837b HTTP/1.1" 200 -
127.0.0.1 - - [14/Jul/2021 11:45:54] "POST /socket.io/?EIO=3&transport=polling&t=NgaQ93n&sid=2c6e85bb23aa4c83af37bc005a08837b HTTP/1.1" 200 -
2c6e85bb23aa4c83af37bc005a08837b: Received packet PING data None
2c6e85bb23aa4c83af37bc005a08837b: Sending packet PONG data None
127.0.0.1 - - [14/Jul/2021 11:46:20] "GET /socket.io/?EIO=3&transport=polling&t=NgaQ94a&sid=2c6e85bb23aa4c83af37bc005a08837b HTTP/1.1" 200 -
127.0.0.1 - - [14/Jul/2021 11:46:20] "POST /socket.io/?EIO=3&transport=polling&t=NgaQFPv&sid=2c6e85bb23aa4c83af37bc005a08837b HTTP/1.1" 200 -

First output even though dataframe is updated.

After reloading the page, the page is blank and then displays correct chart.

What I would like to achieve:

1. Automatically display the bar chart when dataframe is updated without reloading page.

In function(receiving_data) found in the html page , variable plot is used instead of receiving_data. Variable plot is initialized when render_template is evoked. When data is being emitted via sockets, you do not need to pass variable plot when return render_template('views/index_img_soc.html', plot=bar) is called.

See example script below on how to emit data using sockets to the html script.

The script below will automatically update a bar chart without reloading the page.

The code using chart.js instead of plotly. There are much more examples plotting chart.js in javascript as opposed to plotly.

Updated Python script:

import random
from flask import Flask, render_template, session, request
from flask_socketio import SocketIO
from flask_executor import Executor
import pandas as pd
import json
app = Flask(__name__)
app.config['SECRET_KEY'] = 'secret!'
socketio = SocketIO(app)
thread = None



@socketio.on("response_demo")
def background_task_func():
    """Example of how to send server generated events to clients."""

    socketio.sleep(5)
    print("send")
   
    data = {'Name': ['Tom', 'Joseph', 'Krish', 'John','Shadz'], 'Age': [20, 21, 19, 18,36]} 

    data_2= pd.DataFrame(data)
    
    df_json=data_2.to_json(orient='records')
    result = {"objects": json.loads(df_json)}
    socketio.emit('my_response',result, broadcast=True)

@app.route('/')
def index():
    executor.submit(background_task_func)
    return render_template('index_2.html')



if __name__ == '__main__':
    executor = Executor(app)
    socketio.run(app)

Updated html script:

<!DOCTYPE HTML>
<html>
<head>
    <title>Flask-SocketIO Test</title>
    <script type="text/javascript" src="//code.jquery.com/jquery-1.4.2.min.js"></script>
    <script type="text/javascript" src="//cdnjs.cloudflare.com/ajax/libs/socket.io/1.3.5/socket.io.min.js"></script>
    <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.5.0/Chart.min.js"></script>
    <script src="//cdnjs.cloudflare.com/ajax/libs/socket.io/2.2.0/socket.io.js" integrity="sha256-yr4fRk/GU1ehYJPAs8P4JlTgu0Hdsp4ZKrx8bDEDC3I=" crossorigin="anonymous"></script>

</head>

<canvas id="myChart" width="100" height="100"></canvas>
    <script type="text/javascript" charset="utf-8">

// Chart.js Bar Chart
var ctx = document.getElementById("myChart");
var myChart = new Chart(ctx, {
    type: 'bar',
    data: {
        labels: ["Red", "Blue", "Yellow", "Green", "Purple"],
        datasets: [{
            data: [2, 2,2, 2,2],
            backgroundColor: [
                'rgba(255, 99, 132, 0.2)',
                'rgba(54, 162, 235, 0.2)',
                'rgba(255, 206, 86, 0.2)',
                'rgba(75, 192, 192, 0.2)',
                'rgba(153, 102, 255, 0.2)'
            ],
            borderColor: [
                'rgba(255,99,132,1)',
                'rgba(54, 162, 235, 1)',
                'rgba(255, 206, 86, 1)',
                'rgba(75, 192, 192, 1)',
                'rgba(153, 102, 255, 1)'
            ],
            borderWidth: 1
        }]
    },
    options: {
        scales: {
 
            yAxes: [{
                ticks: {
                    beginAtZero:true
                }
            }]
        }
    }
});


        $(document).ready(function() {

            var socket = io().connect('http://127.0.0.1:5000');
            socket.emit('response_demo')
            socket.on('my_response', function(obj) {
            for (var i=0; i < obj.objects.length; i++) {
             myChart.data.datasets[0].data[i] =obj.objects[i].Age;
             myChart.data.labels[i] =obj.objects[i].Name;
            
            }
            
                myChart.update();
           
            });

        });

</script>
</html>

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